The invention relates generally to control systems for internal combustion engines, and more particularly, concerns a powertrain controller for drive by wire vehicles.
For xe2x80x9cdrive by wirexe2x80x9d-equipped vehicles such as an electronic throttle control-equipped vehicle a variable valve timing-equipped vehicle, it is necessary to interpret driver demand and convert it to an appropriate engine control command to deliver the desired engine/vehicle response. For example, in U.S. Pat. No. 5,400,865, the driver demand is converted to common control variable selected from throttle angle, airflow or torque to control the engine output. The torque-based scheme arbitrates between multiple requests for powertrain output torque. These output torque requests originate from the driver demand, the speed control system, or the traction control system. Only one of these output power requests, however, is chosen by the control system to regulate the engine output torque. The maximum output power request is arbitrated between the speed control system and the driver demand. If the vehicle is equipped with traction control, the output power request is also limited by the output torque request of the traction control system.
Interpreting driver demand and generating an appropriate engine command, however, is complicated by the existence of other sub-systems including vehicle, engine or transmission constraints such as vehicle speed limits, engine speed limits and transmission speed or torque limits. Accordingly, there is a need for an arbitration scheme which selects the most appropriate engine control parameter from the various requesters. Arbitration schemes that rely upon a common control variable such as torque or airflow may not be suitable for some vehicle and engine systems.
Accordingly, it is an object of the present invention to provide an improved engine output controller.
According to the present invention, the foregoing and other objects and advantages are attained by an engine output control method for a vehicle having a drive by wire engine system responsive to a desired engine speed signal. The method comprises the steps of generating a driver demanded engine speed value corresponding to an operator input and generating a speed control system engine speed value corresponding to a predetermined speed value to permit vehicle operation at a constant speed by a speed control system. The method arbitrates between the driver demanded engine speed value and the speed control system engine speed value to derive a first desired engine speed value. This value is limited by a vehicle speed limit value, engine speed limit value, and transmission speed limit value to generate a second desired engine speed value. The engine is then controlled as a function of the second desired engine speed value and an actual engine speed value. In another aspect of the invention, a traction control value and transmission limiting value are generated in the torque domain and arbitrated against the speed domain-based second desired engine speed value to control the engine output.
In another embodiment of the present invention, values are generated in the acceleration domain to control the engine output. Specifically, values are generated for a driver demanded vehicle acceleration value corresponding to an accelerator pedal position; a speed control system vehicle acceleration value corresponding to a predetermined speed value to permit vehicle operation at a constant speed by a speed control system; a vehicle speed limit acceleration value corresponding to a maximum vehicle acceleration value to achieve a predetermined vehicle speed limit; and a traction control vehicle acceleration value corresponding to a maximum vehicle acceleration value to prevent wheel slip. These values are then arbitrated to derive a first desired vehicle acceleration value. The first desired vehicle acceleration value is limited by an engine speed limit value and transmission speed limit value to generate a second desired vehicle acceleration value. The resulting value can be used to control the engine output directly or converted to a desired engine acceleration value to control the engine output.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims and upon reference to the accompanying drawings.